Many acoustic transducers or drivers use a moving coil dynamic driver to generate sound waves. In most transducer designs, a magnet provides a magnetic flux path with an air gap. The moving coil reacts with magnetic flux in the air gap to move the driver. Initially, an electromagnet was used to create a fixed magnetic flux path. These electromagnet based drivers suffered from high power consumption and loss. Acoustic drivers can also be made with permanent magnets. While permanent magnets do not consume power, they have limited BH products, can be bulky and depending on the magnetic material, can be expensive. In contrast the electromagnet based drivers do not suffer from the same BH product limitations.
Recently, more efficient electromagnet-based acoustic transducers have been developed that incorporate the advantages of electromagnets while reducing the effect of some of their disadvantages. However, in electromagnet-based acoustic transducers, non-linearities in the magnetic flux across the air gap can introduce undesirable artifacts in the sound that is reproduced, There is a need to minimize or eliminate such non-linearities.